The liver is an organ in the abdomen. It is part of the gastrointestinal system. Sometimes people use hepar- or hepat- as a prefix when they talk about the liver.

The liver does many important things in the body:

There are many different liver diseases. Liver disease can make someone very sick because of all the important work the liver does. People who have bad liver disease usually die unless they can get a liver transplant. This is when the liver from someone who has just died is put in another person by surgery. Such surgeries are usually technically challenging but can be life-saving.

The symptoms of liver disease happen because the liver does not do the work it should.

The liver cannot metabolize toxins and waste so these bad things stay in the blood longer. One thing that builds up is a substance called bilirubin. When red blood cells die, the hemoglobin in them leaks into the blood. The hemoglobin becomes bilirubin (a yellow substance that makes bile yellow). The liver takes the bilirubin out of the blood and puts it into the bile. The bile goes into the intestines and then goes out with the waste from your body. If the liver is hurt, it does not remove the bilirubin, so the bilirubin stays in the body. This makes the person's body look yellow and is known as jaundice. So yellow eyes and yellow skin are symptoms of liver disease.

Other symptoms of liver disease are:

Hepatitis is when liver cells get inflamed (sick). This can be from virus infections. This can be caused by toxins or poisons. The most common toxin to cause hepatitis is alcohol. It can also have genetic, or autoimmune causes, when the body's immune system hurts itself.

Cirrhosis is caused by death of liver cells that happens again and again. When the cells die, scar tissue forms. This scar tissue damages the structure of the liver. This makes the liver not work as well. But it also makes the pressure in the veins that go to the liver very high. This high pressure makes esophageal varices. The most common reason for cirrhosis in the world is hepatitis B virus infection.

Some diseases cause bad things to build up in the liver. Hemochromatosis causes extra iron to build up in the liver. Wilson's disease causes extra copper to build up in the liver. Both of these diseases hurt the cells and can cause very bad liver disease that kills people.

You can also get cancer of your liver. This can be metastatic cancer that came from some other place in your body. The liver is a common place to get metastases because it takes bad things out of the blood. So it takes cancer cells out of the blood and they grow in the liver. Cancer can also grow in the liver. If it grows in the liver it is called hepatocellular carcinoma (liver cell cancer). Most hepatocellular carcinoma is from cirrhosis.

Some liver diseases can be treated easily with medicine. Hemochromatosis is treated  by taking blood from people every two months.

Some liver viruses can be stopped before they start. Two types of viral hepatitis can be stopped with an immunization. Hepatitis A and Hepatitis B can be prevented with a total of five shots in a person's life.

Some liver diseases can only be treated with liver transplant.